Microwave electrical testing system



Feb. 2, 1950 W. A. EDSON El' AL MICROWAVE ELECTRICAL TESTING SYSTEMFiled May 11, 1946 l F IG.

2 Sheets-Sheet 1 Feb. 2l, 1950 w. A. EDso n Al. 2,498,073

MICROWAVE ELECTRICAL TESTING SYSTEM FiledrMay 1l, 1946 2 Sheets-'Sheet 2n/.Afoso/v lA/VEA/TORS G. W/LSON @y wwl A T TOR/VE Y Patented Feb. 21,1950 l MICROWAVE ELECTRICAL TESTING l SYSTEM william A. Eason, Atlanta,Ga., and Ira G. wilson; -New York, N. Y., assignors to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a l Corporation of New YorkY Application May 11, 1946, Serial No. 669,046

(Cl. P11-95) 2 claims,

This invention relates to testing equipment and more particularly `toapparatus permitting the rapid checking of the perfomance of objectlocator systems employing reected pulses of electromagnetic waves.

An object of the invention is to provide a compact and efcient microwaveswitch'so shielded.

as to prevent leak in either its open or closed positions from thecircuits which it may serve to -be invariable in its apparent electricallength while being switched from a selective or tuned input circuit to anon-tuned input circuit and vice versa;

An additional object of the invention is to provide a variable couplerfor microwaves which may serve to couple a detector alternately toeither a cavity resonator or a coaxial input circuit while maintainingthe detector effectively disconnected from the other.

Cavity resonators have `many applications in the microwave art. Asphantom targetsA for radio object locators they respondselectively to apulse of incoming oscillations and upon its cessation yield a protractedtrain of oscillations from the energy stored up in an internalelectromagnetic ield. In frequency measuring equipment they may serve inconjunction with a mechanical tuning device andan oscillation detectingand indicating apparatus to measure the frequency of receivedoscillations with a high decree of accuracy. In all these applicationsit is desirable to connect and disconnect them from their associatedtransmission circuits by apparatus which introduces a minimum of energydissipation or reection when in transmission or energy pass conditionand which entirely removes them from the circuit when in non-transmission condition. A

In microwave testing apparatus it is frequently desirable rst to connectthe oscillation detector and current indicator to an untuned inputcircuit -until the presence of oscillations is established by theindicator and then to introduce in lieu of the untuned circuit a highlyselective device such as a variable cavity resonator by means of whichthe frequency of the oscillations may be ascertained. For this purpose asimple and 2 effective microwave switching System which will establishany of the various circuit conditions at will and, at the same time,permit the oscillation detector to operate under substantially un-Achanged electrical conditions is desirable.

' In accordance with the invention an electrical microwave testingsystem is provided with both a non-selective or untuned input circuitand a selective or tuned circuit including a resonant cavity. Themicrowave oscillation detector and the detected energy indicator arebuilt into a unitary mechanical structure with one element of amicrowave switch which may be brought into effective energy transferrelation with either the untuned input circuit path or with the tunedinput path at will.

. In one embodiment, the unitary structure may I remain stationary whilea movable switch or coupling member capable of longitudinal motioncarries into energy transfer relation with the unitary structure eitherthe movable coupling member of the untuned input path or the movablecoupler of the tuned input circuit. In the drawing, Fig. 1 illustratesdi cally a testing. equipment which constitutes one embodiment of theinvention;

Fig. 2 is a section along the plane 2-2 of the structure shown in Fig.1;

, Fig. 3 isla vertical section of a detector indicator apparatus whichdiffers somewhat from that'shown diagrammatically 'in Eg. 1;

a collecting reflector 3 is connected to a coaxial section having aterminal 'plug 5 which may be inserted either in the jack 6 of a tunedinput system or in the jack l of an untuned circuit. The tuned inputcircuit involves a coaxial section 8 coupled by a retractile loop S tothe internal electromagnetic ileld of the cavity resonator I0. Thetuning of the resonator In may be varied at will by va reciprocation ofthe timing pllmger Il and the tuning piston I2 to a positionat which theresonator responds most strongly to oscillations of the desiredfrequency. An aperture I3 in the bottom of the resonator II) enablescoupling of the resonator I0 to a detector and coaxial circuit Il whenthe coupling loop i5,

molmted on a slidable structure capable of longitudinal motion withinthe enclosing guide I6, is actuated to bring the loop I into the dottedposition shownin Fig. 1. In that position the loop Il projects slightlyintothe internal electromagnetic ileld of the resonator Il. The untuned`input circuit comprising the Jack 1, and

the coaxial section I1 terminates in a slidable coupling loop Il which,like a similar slidable loop Il. ismounted in a guided block locatedwithin the shielded casing 23 of the coupling and switching structure.'I'he guide blocks carrying the loops I3 and Il are slidably mountedwithin portions `of the shielded casing 2l in such manner that theymaybe made to approach or recede from apertures opening into the coaxialindicator circuit Il so as to be eilectively coupled with or electivelyuncoupled from that circuit. In the condition shown in Fig. 1 the loopIl of the Auntimed circuit Isin such position as to be effectivelycoupled with the circuit Il and the loop Il o! `the timed circuit issubstantially wholly uncoupled from the circuit I4. The guide blocks aremechanically operated by handle 2| so that with the` handle at itsextreme right position, as shown in Fig. l, the microwave pick-up deviceI is connected through the untuned input circuit II and loop Il with thedetector and indicator circuit Il. When,A however, the plug 5 isinsertedin Jack I and handle 2| is moved to the left the microwavepick-up device will be connected by way of circuit I, loop 3, theresonator Il; `loop Il, coaxial conductor `22 and loop i9. theseconnections constituting `a tuned input circuit because of the selectivecharacteristics of resonator Il, to the detector and indicator circuitIl. It will be imderstood, of course, that in thu position the guideblocks carrying the retractiie lool! 3 and II are in their uppermostpositionssoastoenabletheretractileloopstobe effectively coupled to theelectromagnetic field within resonator Il.

As shown, the coaxial circuit i4 includes a detector or rectiner 23 oi'any preferred type in-` tercaiated in series in the central conductor2l. An apertured disc 2l of dielectric material is interposed betweenclosely adJacent anges 26 of the outer conductor of the coaxial circuitto constitute with the flanges 23 a blocking capacitor for rectinedcurrent which is constrained to pass to the; milliarnmeter 2'I, theblocking capacitor presenting negligible impedance in circuit II to highfrequency currents of the oscillation freqikncy. An integrating orsmoothing-.condenser 23 is provided in shunt to the'milliammeter 21 inwell-known manner.

The coaxial circuit Il, 24 is of approximately a halt: wavelength.Accordingly, circuit I4, 24 presents` a very low impedance. Because ofthe low impedance of the half wavelength coaxial section. theelectromotive vforce induced in the central conductor 24 by the inputloop I8 or i9, as the casemay be, is expended primarily across theterminals of the detector 23. The unidirectional current produced `asthe result of the rectifying action of the detector 23 passes to themilliammeter 21 which accordingly provides a convenient and sensitivemeans for indicating the intensity of the oscillations supplied by thecouplingloop Il or I3. The relatively large integrating condenser 2lhaving a capacitance of the order of a microiarad serves to smooth thecurrent to the meter 21 in case the high frequency m13! 18 Supplied inthe iorm oi intermittent to compensate for its reactive component. Thismay be done by modifying the length oi the coaxial structure fromthe'half wavelength so as to obtain the eilect of either an inductive ora capacitative reactance in series with the detector.

In this manner it is possible to obtain the full resonance electromotlveforce for application to the detector 23 and, accordingly, to improvethe sensitivity of the device or to increase the constancy oi' thesensitivity with respect to frequency.

As indicated tically in Fig. 2, the principal planes of the loops 0 andI5 are in a tangential direction with respect to the circular electricfield by TEO-m oscillations. This makes for an eiective coupling withilelds of that type and serves to minimize couplings to ilelds of otherundesired modes of oscillation.

The-disclosure of Figs. 1 and 2 is oi diagrammatic character in order toillustrate the principles of the invention. A preferred embodiment whichis electrically the equivalent but which permits the structure tov bemadei much` more compact and convenient to operate is disclosed in Figs.3, 4 and 5. In the apparatus of these gures a microwave pick-up system|0l and the cavity resonator ||0 may be identical with the microwavepick-up I and cavity resonator i0 respectively of Fig. 1. Thereciprocating structure including the handle I2| and the slidable loopsIII and IIS are identical with the corresponding i elements of Fig. lexcept that the loops lie in a horizontal plane perpendicular to thepaper. This permits the coaxial section Il, |24 to be placed in ahorizontal position parallel and very closely adjacent to the bottom ofthe cavity resonator IIII instead ofin the perpendicular positionindicated in the diagram-ot Fig. 1. The shielded casing |20 mayaccordingly be attached directly to the bottom of the cavity resonator.To the rear of the casing |20, as viewed in Fig. 3. are enclosing guides||6 also attached to the underside of the cavity resonator ||0. Withinthe guides IIB are movable guide blocks |30 and |3| which are movable ina vertical direction to bring the loops |00 and IIS into coupling.relation with the interior electromagnetic field of the resonator I0, asshown i'n the case of loop Il! in Fig. 3 or out oi coupling relationtherewith as shown in the case o'f loop H5. The loop |33 is adjusted inposition by means of knob |32,`shait |33 and the yoke |34' carried byshaft |33 astride the pin |35 projecting from the guide block |30.Rotation of the knob |32 with corresponding rotation of the yoke |34carries the pin |35 and its associated guide block |30 in a verticaldirection, the pin being free to slide vertically in a slot |36.' Theloop I5 and the guide block 3| upon which it is mounted are similarlyreciprocated bymeans of a pin |31 projecting from the guide ,block |3|amil operated by a yoke |38 which constitutes one arm of a'bell 4cranlr|39 pivotally mounted at |40, the other arm of the -bell crankcomprising a similar yoke III operated by a projection |42 integral andextending upwardly from the reciprocating handle |2|. It follows thatwhen the handle |2| is moved to the right to bring the coupling loop I8into coupling engagement with the coaxial section, the bell crank |30 isrotated in counter-clockwise direction to withdraw loop ||5 from theinterior of the ,cavity resonator I0 into the position in which it isshown in full linein Fig. 3. At the same time the reciprocatingmechanism carries the loop Il! to a position remote from the coaxialsection.

Conversely. displacement of the handle |2| toward the left upcouples theloop ||8 and couples the loop ||9 to the coaxial section andsimultaneously moves the loop |I5 into coupling position with theinterior electromagnetic iield of resonator and the loop H9 intocoupling with the coaxial section lil, |24. In this latter or tunedinput position the operator will, of course, rotate the knob |32 touncouplethe loop |09 from the cavity resonator and will transfer blockfrom jack |01 to jack |06.

The details of tle detector |23 are illustrated in Fig. 4 in which aportion of the vitreous cylinder I is broken away to show the minutecrystal plate |45, for example, of silicon, seated on the metal baseplug |46 and in contact with a springpressed metallic point |41 of thecat-Whisker type. The insulating disc |25 electrically separating the|26 iiange of the metallic sleeve |50 from the outer coaxial member I I4is secured mechanically to the member H4 by insulating mechanicalconnections, not shown. A metal cap |5| is attached by av screw-threadedconnection to the end of sleeve |50 and serves the double purpose ofexcluding dust and moisture from the coaxial section H4, |24 and ofcompleting the electric circuit through the circular block |52 which isgripped rmly between the cap |5| and the base member on which thedetector plate |45 is mounted. The detector cartridge consisting of thetubular insulating member |44, its terminal blocks and encloseddetector, is accordingly held iirmly with its central axis inlongitudinal alignment of the inner conductor |24.

It will be apparent that the structure which has been disclosed providesa stable xed mounting for the sensitive crystal detector, together witha convenient switching mechanism for connecting the pick-up antenna toVthe detector either through the tuned input system including theresonant chamber or through the untuned input system. It is, therefore,possible to quickly ascertain the presence of microwave oscillations ofa frequency within the range of the resonator by rst using the untunedinput system. After the presence of such microwave has been ascertainedthe apparatus may be quickly and easily switched to the tuned inputcircuit to permit determination of the size wavelength by manipulationof the tuning piston in well-known manner.

The apparatus described is very useful as a wave meter for microwaves.It may also serve with the pick-up system connected to the tuned inputand with the handle |2| in its extreme position to the left to uncouplethe loop I5 and with the shaft |33 rotated in counter-clockwise positionto disconnect the loop |09 vas an echo box for receiving pulses ofmicrowave energy and reradiating the energy over the pick-up antennaafter the incoming pulse has terminated.

What is claimed'is:

1. A microwave detecting system comprising a closed hollow `casing ofelectrically conductive material, a fixed coupling element mountedtherein, a detector connected to the coupling element and a meterconnected to the detector and a pair of movable coupling elements alsomounted in said casing for simultaneously reciprocating motion thereinand means for moving said movable elements to bring one or the otherselectively into energy transfer relation with the iixed couplingelement.

2. A microwave detecting system comprising a i closed hollow casing ofelectrical conductive material, a fixed coupling loop mounted therein, a

, detector connected to the terminals of the loop and a meter connectedto the detector, a pair of movable coupling loops also mounted Withinthe casing and mechanically connected, a pair of relatively widelyseparated movable loops also mounted in the casing for jointreciprocating motion therein and means for moving said movable loops tobring one or the other selectively into energy transfer relation withthe xed loop.

WILLIAM A. EDSON. IRA G WILSON- REFERENCES CETIED The followingreferences are of record in the file of this patent:

